The general area of concern of the present invention is the accurate control of the planting or tilling depth, for example, of an implement in which the planting, tilling, etc., tools are carried by a frame drawn by a tractor. The typical frame is supported on cranked axles under control of a hydraulic cylinder extended and retracted selectively according to suitable valve mechanism in response to departures of the tools from a preselected attitude or depth. The valve response may be to a ground feeler, gage wheel or equivalent sensor, and it is desirable that the response be accurate and properly sensitive. Many types of sensors and controls have been used heretofore, including hydraulic, electro-hydraulic, etc. All of these have one or more short-comings, including inaccurate response, sluggishness, complexity and short life, among others.
The principal purpose of the present invention is to provide significant improvements in a hydraulic system employing a sensor-responsive depth regulator having a four-position valve spool connected into the existing tractor hydraulic system and initially under control of a manual selective control valve operative by the tractor driver, for example. The selective control valve is movable to either of two active positions respectively at opposite sides of a neutral position and, in one of these active positions, conditions the depth regulator valve for raise and lower responses to the sensor. The depth control valve is so constructed that as a result of changing the selective control valve to its other active position, the depth control valve is capable of producing a fast-raise mode, as when raising the implement to transport.
It is a further feature of the invention to provide a system incorporating a hydraulic lockout for preventing leak-down of the lift cylinder when the implement is, for example, in transport mode. This lockout serves also as a pressure-openable check valve for enabling lowering of the implement.
A still further feature of the improved depth control valve is the association with the valve spool of a pressure-receivable chamber to which a pressure-receiving area of the valve spool is exposed. In conditions requiring fast-raise operation of the control valve, as raising of the implement to transport position, the tractor valve is actuated to reverse the pressure and return ports in the depth control valve and the chamber becomes pressurized. In the other operational mode of the depth control valve, the spool is subjected to varying spring pressures at opposite ends. In the fast-raise mode, the pressure is added to the one spring to shift the valve as required. An arrangement of this type simplifies the hydraulics and enables the depth control valve to be used with existing tractor-systems.
The invention has for a further feature provision for using the valve with either open- or closed-center hydraulic systems. In the present case, only a simple change of appropriate hydraulic control cartridges is required.
The foregoing and other features and advantages of the invention will become apparent as a preferred embodiment thereof is disclosed hereinafter .